Field of the Invention
The present invention relates in general to the supply of inductive loads, and more especially to the measurement and detection of one or more anomalies in the bonding resistances of a switching structure such as a transistor bridge, for example, adapted to drive a current of determined value in an inductive load.
Description of the Related Art
The invention finds applications particularly in the field of automobiles. It may be used, for example, to control switching connectivity structure(s) such as an H bridge. Such structures are used to control the direction and/or strength of the electric current in inductive loads, for example electric motors. These motors may be used in electronic control systems of an actuator, such as an electronic throttle control (ETC), or more generally any other equipment actuated by an electric motor, such as a power window.
FIG. 1 schematically illustrates control of an inductive load 10 (electric motor or the like) taking place in a known manner with the aid of a switching structure 2 (of the H bridge type). Such a switching structure 2 comprises in particular four power switches HS1, HS2, LS1 and LS2, each switch being formed in general by an MOS (Metal Oxide Semiconductor) power transistor. These four transistors are managed in a “control” layer of the system, coming above a “component” layer consisting of the electronic components per se of the H bridge. A sequence of control signals for each of the transistors is produced according to a determined strategy, for example on the basis of a setpoint control signal. This strategy causes the H bridge to be controlled in certain determined configurations with the aid of sets of controls leaving certain combinations or certain sets of controls unused.
The components which constitute the control structure of the H bridge are generally integrated into packages referred to as integrated circuits. Such circuits are designed with the aid of design and assembly techniques derived from microelectronics. With a view to increasing performance and reducing costs, integrated circuits in general, and in particular integrated circuits intended for the automobile industry, are faced with a constant need to reduce their size and increase their integration and their performance, which may sometimes cause problems of overheating in the circuits.
One source of heating in an integrated circuit, such as an H bridge 2 illustrated in FIG. 1, is the connection of this circuit to terminals for access to the circuit, for example in order to supply it with electricity and connect it to the corresponding load. In the case illustrated in FIG. 1, the transistors HS1, HS2, LS1 and LS2 are connected on the one hand to a battery 3 delivering a voltage Vbat and to a reference voltage such as a ground GND, and on the other hand to the inductive load 10. In each case, a connection referred to as a bond 6 is produced between a point of connection 4 between two transistors and a terminal 8 for access to the H bridge 2. These bonds 6 introduce resistances into the circuit, which then release heat by the Joule effect during the operation of the circuit.
A plurality of connection techniques are possible and are well known to the person skilled in the art, for example the technique of connection with the aid of conductive wires called wire bonding, using metal wires to connect the various components. In order to optimize the bonds between the various elements and/or make them more reliable, it is possible to use a plurality of connection wires, which are then connected in parallel.
During the control of a motor, for example, predetermined combinations activate certain pairs of control transistors of the H bridge 2 and cause currents of varying strength to flow through the corresponding connection wires, which may generate overheating due to the passage of a strong current. This overheating causes a localized increase in the temperature, principally at the connection wires, and generates a relatively large variation in the internal resistance of the connection wires in question, in certain cases causing them to break.
If a connection wire is poorly connected, the overall resistance of the corresponding bond, also referred to as a contact resistance, is affected. Ideally, good connection of each connection wire should be checked, for example by measuring the corresponding contact resistance. It is necessary to be able to test the bonds separately and independently, in order to identify whether at least one wire is defective.
The bonding resistances may be estimated theoretically on the basis of knowledge of the length (maximum value for the worst case) and the diameter (minimum value for the worst case) of the wires used, the material used being known. The maximum theoretical value may be used as a comparison reference for the measurement.